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How to estimate alfalfa quality in the field using PEAQ
You can estimate alfalfa relative feed value (RFV) and neutral detergent fiber (NDF) levels with the Predictive Equations for Alfalfa Quality (PEAQ) system, which gives alfalfa producers a simple way to schedule harvests. A PEAQ stick can be a useful tool when implementing this approach.
How to estimate alfalfa relative feed value (RFV)
This procedure estimates alfalfa RFV of the standing crop. It doesn’t account for changes in quality due to wilting, harvesting and storage. These factors may further lower RFV by 15 to 25 points, assuming good wilting and harvesting conditions.
This procedure is most accurate for good stands of pure alfalfa with healthy growth.
- Choose a representative 2-square-foot area in the field.
- Determine the most mature stem in the 2-square-foot sampling area using the criteria shown in Table 1.
- Measure the length of the tallest stem in the 2-square-foot area. Measure it from the soil surface (next to plant crown) to the tip of the stem (not to the tip of the highest leaf blade). Straighten the stem to accurately measure its length. The tallest stem may not be the most mature stem.
- Based on the most mature stem and length of the tallest stem, use Table 1 to determine the standing alfalfa forage’s estimated RFV content.
- Repeat steps 1 to 4 in four or five representative areas across the field. For fields larger than 30 acres, sample more times.
The general recommendation is to harvest when the PEAQ estimate or the scissors cut sample lab test is 15 to 25 RFV points higher than what you want to have in the feed manger.
RFV by stem height and plant stage
Height | Late vegetative | Bud stage | Flower stage |
---|---|---|---|
16 inches | 237 RFV | 225 RFV | 210 RFV |
17 inches | 230 RFV | 218 RFV | 204 RFV |
18 inches | 224 RFV | 212 RFV | 198 RFV |
19 inches | 217 RFV | 207 RFV | 193 RFV |
20 inches | 211 RFV | 201 RFV | 188 RFV |
21 inches | 205 RFV | 196 RFV | 183 RFV |
22 inches | 200 RFV | 190 RFV | 178 RFV |
23 inches | 195 RFV | 185 RFV | 174 RFV |
24 inches | 190 RFV | 181 RFV | 170 RFV |
25 inches | 185 RFV | 176 RFV | 166 RFV |
26 inches | 180 RFV | 172 RFV | 162 RFV |
27 inches | 175 RFV | 168 RFV | 158 RFV |
28 inches | 171 RFV | 164 RFV | 154 RFV |
29 inches | 167 RFV | 160 RFV | 151 RFV |
30 inches | 163 RFV | 156 RFV | 147 RFV |
31 inches | 159 RFV | 152 RFV | 144 RFV |
32 inches | 155 RFV | 149 RFV | 140 RFV |
33 inches | 152 RFV | 145 RFV | 137 RFV |
34 inches | 148 RFV | 142 RFV | 134 RFV |
35 inches | 145 RFV | 139 RFV | 131 RFV |
36 inches | 142 RFV | 136 RFV | 128 RFV |
37 inches | 138 RFV | 133 RFV | 126 RFV |
38 inches | 135 RFV | 130 RFV | 123 RFV |
39 inches | 132 RFV | 127 RFV | 121 RFV |
40 inches | 129 RFV | 124 RFV | 118 RFV |
How to estimate alfalfa neutral detergent fiber (NDF)
This procedure estimates alfalfa NDF content of the standing crop. It doesn’t account for changes in quality due to wilting, harvesting and storage. These factors may further raise NDF content by three to six units, assuming good wilting and harvesting conditions.
This procedure is most accurate for good stands of pure alfalfa with healthy growth.
This approach uses PEAQ with a simplified staging scale:
- Choose a representative 2-square-foot area in the field. This will be the sampling area.
- Determine the most mature stem in the sampling area using the criteria shown in the table.
- Measure the length of the tallest stem in the sampling area. Measure it from the soil surface (next to plant crown) to the stem’s tip (not to the tip of the highest leaf blade). Straighten the stem to accurately measure its length. The tallest stem may not be the most mature stem.
- Based on the most mature stem and length of the tallest stem, use the table to determine the estimated NDF content of the standing alfalfa forage.
- Repeat steps 1 to 4 in four or five representative areas across the field. For fields larger than 30 acres, sample more times.
NDF based on stem length and plant stage
Length of tallest stem | Late vegetative | Bud stage | Flower stage |
---|---|---|---|
16 inches | 28.5% NDF | 29.7% NDF | 31.4% NDF |
17 inches | 29.2% NDF | 30.4% NDF | 32.0% NDF |
18 inches | 29.9% NDF | 31.1% NDF | 32.7% NDF |
19 inches | 30.6% NDF | 31.8% NDF | 33.4% NDF |
20 inches | 31.3% NDF | 32.5% NDF | 34.1% NDF |
21 inches | 32.0% NDF | 33.2% NDF | 34.8% NDF |
22 inches | 32.7% NDF | 33.9% NDF | 35.5% NDF |
23 inches | 33.4% NDF | 34.6% NDF | 36.2% NDF |
24 inches | 34.0% NDF | 35.3% NDF | 36.9% NDF |
25 inches | 34.7% NDF | 35.9% NDF | 37.6% NDF |
26 inches | 35.4% NDF | 36.6% NDF | 38.3% NDF |
27 inches | 36.1% NDF | 37.3% NDF | 38.9% NDF |
28 inches | 36.8% NDF | 38.0% NDF | 39.6% NDF |
29 inches | 37.5% NDF | 38.7% NDF | 40.3% NDF |
30 inches | 38.2% NDF | 39.4% NDF | 41.0% NDF |
31 inches | 38.9% NDF | 40.1% NDF | 41.7% NDF |
32 inches | 39.6% NDF | 40.8% NDF | 42.4% NDF |
33 inches | 40.3% NDF | 41.5% NDF | 43.1% NDF |
34 inches | 40.9% NDF | 42.2% NDF | 43.8% NDF |
35 inches | 41.6% NDF | 42.8% NDF | 44.5% NDF |
36 inches | 42.3% NDF | 43.5% NDF | 45.2% NDF |
37 inches | 43.0% NDF | 44.2% NDF | 45.8% NDF |
38 inches | 43.7% NDF | 44.9% NDF | 46.5% NDF |
39 inches | 44.4% NDF | 45.6% NDF | 47.2% NDF |
40 inches | 45.1% NDF | 46.3% NDF | 47.9% NDF |
Note: Quality factors are generally expected to change each day as indicated:
-
RFV declines three to four units per day.
-
Relative Forage Quality (RFQ) declines four to five units per day.
-
NDF declines 0.5 percent per day.
-
NDF digestibility (NDFD) declines 0.5 percent per day.
Reviewed in 2018